Evidence for CO Disproportionation over Ceria during Oxygen Storage Capacity Measurements: an in Situ Raman Spectroscopic Investigation

Abstract

The interaction of CO with ceria under conditions typical for oxygen storage capacity (OSC) measurements of three way catalysts (TWC) has been investigated by in situ Raman spectroscopy. It has been shown that CO disproportionates over ceria at 623 K to deposit disordered carbon nano-crystallites, with calculated average crystal size of less than 20 Å. Exposure of the carbonized ceria to gaseous O2 at room temperature resulted in the disappearance of the bands attributed to the carbon in Raman spectra, accompanied by the emerging of bands of surface formates, carbonates, and adsorbed peroxide species. Even though the kinetics of the ceria-catalyzed CO disproportionation reaction has yet to be measured, the present investigation suggests that the generally accepted procedure for OSC measurements of TWCs results in an OSC overestimation and, hence, needs to be reconsidered.